JP3308489B2 - Casting method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a casting method and a casting apparatus for small articles such as dental articles and accessories, and more particularly to a casting apparatus for melting a metal material by high-frequency induction heating and pouring it into a mold. is there.

[0002]

In casting, there is an appropriate casting timing for pouring for each metal to be melted. If it is earlier than the proper casting timing, the viscosity of the molten metal becomes high, and it is impossible to produce a precise casting without reaching every corner of the mold. Conversely, if the casting time is later than the proper casting timing, the casting temperature will be too high and the metal itself will evaporate, oxidize, change its composition, and seize on the mold when it is poured into the mold. May be. Therefore, an error in the casting timing is large, which affects the quality of the cast product.

[0003] Conventionally, in order to grasp the pouring timing of such a casting apparatus, a skilled person having many years of experience visually observes the molten metal, and the entire metal block is reduced to an appropriate viscosity. At present, the casting timing is determined when it is determined that the casting has been performed. In order to automatically detect and pouring this metal, it is automated by detecting the surface temperature of the metal using an infrared radiation thermometer, utilizing the fact that the appropriate casting timing is correlated with the temperature of the metal. There is a way to do that. However, the emissivity of infrared rays differs depending on the metal, the emissivity changes due to the surface condition changing during melting, and the surface film of the metal starts melting and the viscosity starts to decrease. Because the (e.g., oxide film) is partially scattered and floats and moves, the infrared emissivity of the metal surface fluctuates irregularly, and depending on the metal, evaporation or gas generation may cause absorption and attenuation of infrared light. Therefore, it is difficult to accurately detect the surface temperature.

[0004] Furthermore, in casting, it is not always the case that a new metal is used, but the metal in the surplus part of the cast product is often cut out and reused to be melted. At that time, the oxide on the metal surface is thickened. In addition, the detection of metal temperature is impaired. In addition, since the infrared radiation thermometer measures one point on the surface of the metal, it cannot measure the internal temperature. Therefore, it is difficult to determine whether or not the entire metal has completely reached the proper casting temperature and has decreased to the proper viscosity. For the above reasons, the method using the infrared radiation thermometer has a drawback that the error in the detected temperature becomes large, the casting timing becomes inaccurate, and it is not possible to cope with a wide range of metals and conditions.

[0005] In addition, taking advantage of the fact that when a metal is melted and liquefied by heating, it changes from the outer shape of a solid,
There is a method of simply detecting a change in outer shape and trying to automate it. However, depending on the type of the metal, the oxide film on the surface is very thick or hard, and even when the inside is sufficiently melted, the change in the outer shape is very small, and detection may be difficult. Also, when a metal to be reused is melted, the oxide film is similarly relatively thick, so that it is often difficult to detect the change in shape. For this reason, the metal is heated and boiled more than necessary, and casting defects occur. Furthermore, when a plurality of small metal lumps are put into a crucible and melted, each metal lump is separately melted and liquefied. Cannot be detected. Thus, it is difficult to realize reliable automatic casting under a wide range of conditions.

As described above, in determining the timing of casting, changes in the surface temperature and outer shape of the metal are secondary, and it is necessary to determine whether or not the entire molten metal has an appropriate viscosity. It turned out to be necessary. Thus, the present invention seeks to determine the casting timing by identifying the viscosity of the entire molten metal.

[0007]

According to the present invention, there is provided a high-frequency wave for melting a metal in a crucible by induction heating.
As the current, a high-frequency current whose amplitude is modulated by a low frequency , which changes the shape of the molten metal, is used. As a low frequency for modulating the high frequency current, a rectangular wave or any other waveform can be used in addition to a sine wave. If a square wave is used, its duty cycle is arbitrary.

In metal melting by high-frequency induction heating, when the metal begins to melt, the induction heating current becomes a spherical shape due to electromagnetic force at a certain value or more, and the molten metal is agitated inside the entire shape and gradually becomes uniform. To melt. (Here, there is also a method in which the entire metal ball is floated by further increasing the induction heating current.) This is also a feature of the high-frequency induction heating method. Conversely, when the induction heating current is reduced, the shape of the metal collapses from a spherical shape to a flat plate shape, and the metal simply becomes a shape in which the liquid is contained in the crucible. Utilizing the fact that the shape of metal whose viscosity has decreased can be changed by increasing or decreasing this high-frequency induction heating current, induction heating is performed while forcibly increasing or decreasing the current by applying amplitude modulation by low frequency to the induction heating current. Do.

Although the metal does not change its shape while it is solid, when the metal starts to melt and the surface of the metal decreases in viscosity, a slight change in shape starts to occur in synchronization with the modulation frequency. While the melting has not progressed to the inside, the shape change is small, and only the surface portion changes. As the melting progresses to the inside, the magnitude of the shape change gradually increases, and the shape change of the spherical shape and the flat shape is started alternately. In addition to the spheroidizing and stirring action of the molten metal, which is a feature of high-frequency induction heating, the forcible shape change due to the amplitude modulation frequency of the induction heating current further promotes sufficient stirring, and the entire metal has a faster and more uniform viscosity. Become. The point in time when the magnitude of the shape change exceeds a certain value is determined as the casting timing, and the molten metal is cast into the mold.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS According to the present invention, when the metal in a crucible melts and reaches a state where its shape changes periodically, two types of discrimination of the casting timing based on the amplitude of the shape change are provided. There is a way. The first is a method for visual determination, and the second is a method for automatically determining the shape of a metal by capturing the shape of the metal with an image sensor or the like.

[0011] In the case of visual discrimination, it is not possible to discriminate if the cycle of shape change is too fast, so that the cycle is 0.3 to 1
Seconds are appropriate, and if the cycle is too long, the change in metal temperature for each cycle becomes large, making it difficult to accurately determine the timing. In the case of automatically judging, since the timing can be judged even faster than this, the period of the shape change can be set to about 0.1 to 0.5 seconds.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1, reference numeral 1 denotes a high-frequency induction heating coil, and reference numeral 2 denotes a two-piece crucible, which is vertically divided and poured into a mold 3 below the lower part of the crucible. . Reference numeral 4 denotes a metal to be melted, and reference numeral 5 denotes a two-dimensional image sensor focused on the surface of the metal 4. The coil 1 is connected in parallel with the resonance capacitor 6 and connected to the secondary side of the matching transformer 7. A primary side of the matching transformer 7 is connected to an output side of an inverter 8 for high-frequency induction heating, and an input side thereof is connected to an output side of a DC output voltage control type rectifier circuit 9 composed of a thyristor or the like. The input side of the rectifier circuit 9 is connected to a commercial power supply 10.

The rectifier circuit 9 is provided with a rectifier control circuit 11 for controlling the output voltage of the inverter 8 to be a constant voltage. A low-frequency signal (for example, about 2 to 10 Hz) is applied to the rectifier control circuit 11 from the low-frequency transmission circuit 12, and the low-frequency signal causes the reference signal for constant voltage control of the rectifier control circuit 11 to have a constant amplitude. Modulated. For this purpose, the actual output voltage of the inverter 8 is amplitude-modulated by the frequency and amplitude of the low-frequency signal. Therefore, coil 1
Is similarly amplitude modulated. Inverter 8
Is provided with an inverter control circuit 13. The inverter control circuit 13 detects an output voltage and an output current of the inverter 8, and controls the inverter 8 so as to match the resonance frequency of the tank circuit 14 including the induction heating coil 1 and the capacitor 6. Tracking control of operating frequency.

An analog signal of the image data in the crucible 2 detected by the two-dimensional image sensor 5 is A / D converted by an A / D conversion circuit 15 and temporarily stored in an image storage device 16 as image digital data. . A microcomputer (hereinafter referred to as a CPU) 17 includes an image storage device 16.
A brightness distribution histogram of the metal which is heated and emits light is created from the data of the above, an average value of the brightness is obtained from the histogram, and the value is used as a threshold value to convert the image data into two.
By binarizing, a two-dimensional outline image of only the metal part is extracted. Then, the binarized image data is stored in the binarized image storage device 18. Further, the center of gravity of the outline image 20 is obtained from the stored data as follows.

In FIG. 2, the outer shape image 20 is divided into upper and lower parts, and the number of pixels in each half is counted to obtain an XX line in which the number of pixels in both halves is equal. The YY line in which the number of pixels in both halves is equal is obtained by counting the number of pixels in each half by dividing into two.
-It can be obtained as the intersection of the X-ray and the Y-Y line.

Next, as shown in FIG. 3, the diameter A-
A, BB, CC, and DD are obtained, and the variation in the diameter data is detected and repeated. When the variation in the diameter data becomes equal to or less than a certain value, it is determined that the metal outer shape has become substantially circular, and from that point on, the number of pixels included in the outer shape image 20 in the storage data of the binarized image storage device 18 The area is obtained by counting the area, and the area data is stored in the area storage device 19.

The above-described various measurement calculation processes are repeated at a period of 1/60 second of a field period or 1/30 second of an image period, which is common in television and the like. In the storage device 18 and the area storage device 19, the input data is stored in a time-series manner and stored each time, and old storage data after a predetermined time (for example, 2 to 3 seconds) is deleted.

Here, the CPU 17 obtains the amplitude of the area change of the data stored in the area storage device in a time-series manner, and when the amplitude exceeds a set reference value, the amplitude is directed to the crucible operating device 21. And sends out a casting signal. As a result, the lower portion of the crucible 2 opens left and right, and the contained molten metal falls into the mold 3 disposed below the molten metal.

The above-described embodiment describes a method and apparatus for automatically detecting the timing of casting. However, if the high-frequency induction heating power is amplitude-modulated at a low frequency, the molten metal becomes a circular block. As a result, the outer shape changes at the cycle of the modulation low frequency. Therefore, even in a casting apparatus having a simple configuration in which casting is manually performed, the melting state of the metal can be visually recognized as a very simple phenomenon. You will be able to judge.

[0020]

As described above, according to the present invention, casting is performed at an appropriate timing without being affected by the shape of the metal to be melted, the oxidized state of its surface, the surface state at the time of melting, the melting point, and the like. And high quality casting can be performed without the need for years of advanced experience.

[Brief description of the drawings]

FIG. 1 is a block diagram of a casting apparatus embodying the present invention.

FIG. 2 is an explanatory diagram of a center-of-gravity discriminating method in the embodiment.

FIG. 3 is an explanatory diagram of diameter data used in the embodiment.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 high-frequency induction heating coil 2 crucible 3 mold 4 molten metal 5 two-dimensional image sensor 6 resonance capacitor 7 matching transformer 8 inverter 9 rectifier circuit 10 commercial AC power supply 11 rectifier control circuit 12 low-frequency oscillation circuit 13 inverter control Circuit 14 Tank circuit

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-64-24387 (JP, A) JP-A-63-5683 (JP, A) JP-A-6-142895 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) B22D 23/00 B22D 2/00

Claims (3)

(57) [Claims] 1. A crucible, a high-frequency induction heating device for a metal material in the crucible, and a mold into which a molten metal material in the crucible is injected, wherein the high-frequency induction heating device has a heating current Change the shape of the molten metal material
A casting apparatus characterized by using a high-frequency current whose amplitude is modulated by a low frequency. 2. A two-dimensional image sensor arranged to detect a shape of a metal material in the crucible, and detecting an area change occurring in the metal melt detected by the image sensor in synchronization with the low frequency. 2. The casting apparatus according to claim 1, further comprising means for automatically injecting the molten metal from the crucible into the mold when the amplitude of the area change reaches a certain value or more. . 3. Induction heating of a metal material in a crucible by a high-frequency current amplitude-modulated by a low frequency, and observing a change in area of the metal material synchronized with the low frequency, thereby observing the melting of the metal material. Determine the casting time,
A casting method, wherein the melt is injected into a mold by manual operation.